.Affix_demo{
    .red{
        width: 20px;
        height: 1000px;
        background-color: red;
    }
    //
    .scrollable-container{
        position: relative;
        height: 100px;
        overflow-y: scroll;
        .background{
            padding-top: 60px;
            height: 300px;
            background-image: url(https://zos.alipayobjects.com/rmsportal/RmjwQiJorKyobvI.jpg);
        }
    }
}